When DAK opens very early, the two major walking trails (Gorilla Falls and Jungle Trek) do not open with park opening. Neither do Kilimanjaro Safari nor the train back to Rafiki's Planet Watch/Conservation Station. The animals have a normal routine & schedule when they are typically let out of the barns and are given access to the exhibit areas. For example, this week when DAK opened at 7:30 AM to all guests (early entry of 7 AM for on-site guests), the safari did not begin operation until 8:30 AM and the train and some walking paths opened even later (c. 9 AM). You will also find limited food and drink options during those earlier hours of operation.
That said, we still enjoy going in early. The park is far less crowded in the early morning, and many areas are peaceful and quiet. Some of the smaller paths (such as those around the Tree of Life) are open. And you will often have more of an opportunity to talk to the animal care staff as they prepare the exhibit habitats, set out treats, and release the animals from backstage enclosures. We had an amazing conversation with one of the keepers at the Siamang exhibit yesterday, for example -- learned all about "Veruca" & "Charlie", some of their unique behaviors & personality traits, and plans for a future Siamang family group.